1. Field of the Invention
This invention relates to gas turbine engine rotor seals with teeth such as labyrinth seal teeth and, more particularly, to such teeth having localized compressive residual stresses imparted by laser shock peening and repaired seals with teeth rebuilt by welding.
2. Description of Related Art
A variety of stationary and rotating seals, often referred to as the labyrinth type, are used in various parts of a gas turbine engine. During manufacture, operation, maintenance, etc., such seals, which include one or more projections or teeth connected with a support structure, can be worn or damaged.
It has become common practice to repair in a relatively cost effective manner certain types of such seal teeth or projections by first removing the damaged portion of the tooth. The same material of the tooth then is reapplied as by welding, with excess added material being removed, such as by machining, to regenerate the tooth. Methods and apparatus for conducting such repair is described in U.S. Pat. No. 4,657,171 by Bertrand G. Robins, issued Apr. 14, 1987. As is described in this and other patents referenced therein, a filler material in wire form is moved in a reciprocating manner into and out of a weld pool created by a heating source such as an electric arc to build up the teeth.
Poor weldability, including poor weld flow characteristics and crack sensitivity of the metal from which the projection or tooth is made, characterizes seal teeth repaired in this manner and often prevents repairs in a practical manner or limits the useful operating life of the components thus repaired. Accordingly, when damaged, the costly member may be replaced rather than repaired. The weldment repairs forms a heat affected zone which is that portion of the base metal which was metallurgically altered due to the welding heat. The heat affected zone also is very crack sensitive and, therefore, reduces the useful operational life of the repaired part. Therefore, it is highly desirable to improve the crack sensitivity of the heat affected zone as well as that of the part itself. The present invention incorporates laser shock peening to accomplish this and provide an improved weld repair and article therewith.
Laser shock peening or laser shock processing, as it is also referred to, is a process for producing a region of deep compressive residual stresses imparted by laser shock peening a surface area of a workpiece. Laser shock peening typically uses multiple radiation pulses from high power pulsed lasers to produce shock waves on the surface of a workpiece similar to methods disclosed in U.S. Pat. No. 3,850,698, entitled "Altering Material Properties"; U.S. Pat. No. 4,401,477, entitled "Laser Shock Processing"; and U.S. Pat. No. 5,131,957, entitled "Material Properties". Laser shock peening, as understood in the art and as used herein, means utilizing a laser beam from a laser beam source to produce a strong localized compressive force on a portion of a surface by producing an explosive force by instantaneous ablation or vaporization of a painted or coated or uncoated surface. Laser peening has been utilized to create a compressively stressed protection layer at the outer surface of a workpiece which is known to considerably increase the resistance of the workpiece to fatigue failure as disclosed in U.S. Pat. No. 4,937,421, entitled "Laser Peening System and Method". These methods typically employ a curtain of water flowed over the workpiece or some other method to provide a confining medium to confine and redirect the process generated shock waves into the bulk of the material of a component being LSP'D to create the beneficial compressive residual stresses.
Laser shock peening is being developed for many applications in the gas turbine engine field, some of which are disclosed in the following U.S. Pat. No. 5,525,429, entitled "Laser shock peening surface enhancement for gas turbine engine high strength rotor alloy repair"; U.S. Pat. No. 5,675,892, entitled "Laser shock peening for gas turbine engine vane repair"; U.S. Pat. No. 5,591,009, entitled "Laser shock peened gas turbine engine fan blade edges"; U.S. Pat. No. 5,492,447, entitled "Laser shock peened rotor components for turbomachinery"; and U.S. Pat. No. 5,674,329, entitled "Adhesive tape covered laser shock peening" as well as others.